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N Ropert

Publications and source records attributed to N Ropert.

35 records · Page 2Linked to original sources
PubMed1983

Hemicholinium impairs septo-hippocampal facilitatory action.

Intraventricular injections of hemicholinium-3 led to a sharp reduction in hippocampal acetylcholine content (by 79% on the average). This was associated with the following changes in population spikes evoked in area CA1 by commissural stimulation: (1) a tendency to progressive increase, over 1-2 hours; (2) in a few cases (3 out of 12), a striking depression of the normal strong facilitation produced by brief tetanic stimulation of the medial septum (typically 10 pulses at 50-100 Hz); (3) a much more consistent tendency towards fading of the septal facilitatory effect during repeated applications of such brief septal tetani (in 10 cases out of 12); as well as, (4) diminished facilitation by sustained, lower frequency septal tetanic stimulation (20-50 Hz). The reduced efficiency of septal action--especially during repetitive stimulation--was not accompanied by a consistent reduction of the facilitation produced by local applications of acetylcholine; it is, therefore, best explained by the diminished availability of acetylcholine, and so provides further evidence that septo-hippocampal facilitation is mediated by a cholinergic mechanism.

Acetylcholine↗
PubMed1982

Zona incerta and lateral hypothalamic afferents to the midbrain reticular core of cat--HRP and electrophysiological study.

The zona incerta (ZI) and lateral hypothalamic afferents to the midbrain reticular formation (MRF) of cat were investigated with the horseradish peroxidase (HRP) technique and by using antidromic identification in experiments on chronically implanted, behaving preparations. Following HRP injections restricted to the MRF territory (nucleus cuneiformis and central tegmental field), the largest number of retrogradely labeled cells appeared in the medial third of the ipsilateral ZI. Labeling extended medially to the adjacent lateral hypothalamus. The number of positive elements gradually diminished towards the lateral extremity of the ZI and continuing reticularis thalamic nucleus. Ventral lateral geniculate neurons were consistently labeled. No positive elements were found in ventrobasal, pulvinar-lateralis posterior and ventralis lateralis thalamic nuclei. The MRF-evoked antidromic invasion of ZI cells occurred with a sharp mode between 0.5 and 0.75 ms (median latency of the whole sample: 0.6 ms). The conduction velocity of the ZI leads to MRF axons is twice as high as the values found in the reciprocal MRF leads to ZI projection. In addition to the antidromically elicited discharges, MRF stimulated resulted in short-latency synaptic excitation, sometimes following the antidromic invasion of the same neuron. The difference between the discharge rates of ZI neurons during EEG-desynchronized and EEG-synchronized behavioral states was not significant. A statistically significant increase in firing rates was found in ZI neurons during waking periods with movements compared to quiet, motionless epochs of waking. The possible involvement of caudally projecting ZI cells in the preparation of postural and/or phasic motor functions is discussed.

Afferent Pathways↗
PubMed1982

Dye-coupling between pyramidal cells of rat hippocampus in vivo.

Lucifer Yellow was intracellularly injected into pyramidal cells of rat hippocampus in vivo. In 10 successful staining experiments there were 5 cases of dye-coupling, in which 2-4 cells were stained though only one was injected. These results indicate that dye-coupling and, therefore, presumably electrotonic coupling, occurs between neurons of the hippocampus in the whole animal and confirms previous findings in the hippocampal slice in vitro.

Animals↗
PubMed1982

Firing rates and patterns of midbrain reticular neurons during steady and transitional states of the sleep-waking cycle.

Spontaneous firing of midbrain reticular formation (MRF) neurons was recorded extracellularly in chronically implanted, behaving cats during steady and transitional states of the sleep-waking cycle. Physiological identification of receiver and/or projection MRF neurons was achieved through orthodromically elicited discharges. Discharge rates of MRF neurons were more than double in waking (W) and active sleep (D) without phasic motor events, as compared to synchronized sleep (S). During behavioral states associated with EEG activation, the increased firing was essentially due to cells exhibiting high discharge rates, located at relatively ventral levels of the midbrain core. MRF neurons with identified rostrally projecting axons were more active during W and D states; their discharge rates were significantly higher than those of caudally projecting cells. The discharge patterns of MRF neurons increasing their firing rates from S to W and D were of the tonic type. First-order analyses showed a negligible proportion of both very short and long interspike intervals in all states, large interval density around the mode especially in W and D, and the smallest variation coefficients in W. Rhythmic firing with a period near the modal interval was detected during W by autocorrelations. The increase in firing rate of MRF neurons from S to W or D took place before overt EEG desynchronization and behavioral manifestations that define stable W or D states. In our sample a statistically significant increase in discharge rate was found about 15 s before the end of S sleep epochs that developed into awakening. The differences between discharge features of MRF neurons during waking and sleep states and those of neurons in other brainstem reticular fields are emphasized. Taken together, these data support, at a cellular level, Moruzzi and Magoun's concept of a rostral reticular substrate that gives rise to impulses leading to tonic activation of the thalamocortical systems.

Animals↗
PubMed1982

Pharmacological characteristics of facilitation of hippocampal population spikes by cholinomimetics.

In rats under urethane anaesthesia, various cholinomimetics, acetylcholine-antagonists and other agents were released iontophoretically in the pyramidal layer of area CA1. Like acetylcholine, a variety of cholinomimetics readily enhanced population spikes evoked by fimbrial-commissural stimulation. Judging by the equipotent iontophoretic currents, the strongest muscarinic agonist was muscarine. Other potent agonists included carbachol, methacholine, propionylcholine, bethanechol and the much slower-acting arecoline, pilocarpine and oxotremorine. Choline was about 5 times weaker than acetylcholine. Though not as effective as acetylcholine, some nicotinic agonists also consistently enhanced population spikes, particularly dimethylphenylpiperazinium and acetylthiocholine. Other nicotinic agents, such as butyrylcholine, nicotine and tetramethylammonium were much less active. Both scopolamine and atropine, given systematically in high doses (10-80 mg/kg), strongly depressed or abolished the action of muscarinic agonists, but to a lesser and more variable extent the action of ACh. They did not antagonize dimethylphenylpiperazinium. When applied iontophoretically, alpha-bungarotoxin, tubocurarine or mecamylamine did not block the action of any of the cholinomimetics. Indeed, in higher doses they tended to promote population spikes (a comparable enhancement was also seen with larger iontophoretic doses of atropine or scopolamine). On the other hand, gallamine and dihydro-beta-erythroidine antagonized muscarine but not dimethylphenylpiperazinium; a less selective block of cholinomimetics was produced by suxamethonium. It was concluded that both muscarinic and nicotinic receptors (or receptors with mixed properties) appear to be involved in the facilitatory action of acetylcholine on population spikes evoked by fimbrial-commissural stimulation.

Acetylcholine↗
PubMed1982

Electrophysiological and pharmacological characteristics of facilitation of hippocampal population spikes by stimulation of the medial septum.

In rats under urethane anesthesia, single shock or tetanic stimulation of the medial septum--which evoked only minimal field potentials--sharply enhanced population spikes evoked in area CA1 by commissural stimulation. An enhancement of population spikes was observed only (a) in areas CA1 and CA2 (adjacent to CA1 in the dorsal hippocampus), but not in the fascia dentata or the deep pyramidal layers CA3 or CA4; (b) in a narrow range of depth, close to the stratum pyramidale; (c) when the intensity of commissural stimulation was of adequate intensity. A comparable facilitation of population spikes was produced at the same sites by microiontophoretic release of acetylcholine. The septal facilitatory action increased in effectiveness with the number of tetanic pulses (up to 10-12) at a given frequency, and it had a maximum at frequencies of 50-100 Hz. It reached a maximum 20-50 ms after the end of septal stimulation, and then decayed slowly, the overall duration being up to 300 ms. The cholinergic nature of the facilitation induced by septal stimulation was confirmed by the parallel potentiation of septal action and that of acetylcholine by physostigmine and their depression by atropine and scopolamine.

Acetylcholine↗
PubMed1982

Depth distribution and mechanism of changes in extracellular K+ and Ca2+ concentrations in the hippocampus.

In the CA1 area of the hippocampus of urethane-anaesthetized rats, the greatest delta[K+]omicron and delta[Ca2+]omicron evoked by repetitive fimbrial-commissural stimulation were always found in the pyramidal cell layer; but there were large increases in [K+]omicron over a wide range of depth, whereas a major fall in [Ca2+]omicron was localized almost exclusively to the level of the pyramidal layer. A sustained focal negative potential was also evoked by fimbrial stimulation; it resembled delta[K+]omicron in time course and depth distribution and therefore probably reflected cellular depolarization caused by increased [K+]omicron. The close correlation between delta[Ca2+]omicron and delta[K+]omicron and the appearance of population spikes (especially in bursts of three to four spikes) indicate that pyramidal cell firing and corresponding K-outward and Ca-inward currents are mainly responsible for the accumulation of K+omicron and the depletion of Ca2+omicron. In CA3 pyramidal areas, delta [K+]omicron and delta[Ca2+]omicron were comparable in magnitude and distribution to changes seen in CA1, but they occurred after a longer latency, and the major delta[Ca2+]omicron had a longer duration, consistent with a more prolonged Ca2+ current.

Animals↗
PubMed1981

Ethyl beta-carboline-3-carboxylate antagonizes the action of GABA and benzodiazepines in the hippocampus.

In urethane-anaesthetized rats, the beta-carboline derivative beta CCE (0.3-1.0 mg/kg i.v.) excited hippocampal pyramidal cells which were inhibited by GABA (applied iontophoretically) and benzodiazepines (applied iontophoretically or intravenously). While benzodiazepines facilitated the action of GABA, the effects of GABA and benzodiazepines were antagonized by beta CCE. This electrophysiological study supports the behavioural observations that beta CCE is a benzodiazepine receptor antagonist.

Animals↗
PubMed1981

Septo-hippocampal pathway modulates hippocampal activity by a cholinergic mechanism.

In rats under urethane, multibarrelled microelectrodes were used to record field responses of CA1 hippocampal pyramids evoked by fimbrial-commissural stimulation. A strong potentiation of population spikes could be obtained by either a local release of ACh or by a brief tetanic stimulation of the medial septum (which by itself evoked only minimal field responses of the hippocampus). Both effects were sharply reduced after intravenous injections of large doses of atropine or scopolamine, indicating that the septo-hippocampal innervation is to an important degree cholinergic and muscarinic. However, since dimethylphenylpiperazinium (a nicotinic ganglionic agonist) can also evoke population spikes, a significant though variable component of this cholinergic action may operate via nicotinic receptors.

Acetylcholine↗
PubMed1976

Visual receptive field types in the nucleus dorsolateralis anterior of the pigeon's thalamus.

Extracellular recordings were made from cells in the dorsolateral thalamus (DLLv, DLLd, DLAmc) of the pigeon, and their receptive field properties analyzed with stationary and moving visual stimuli. One hundred and ten cells were classified as follows on the basis of their responses. I. On-center and off-center cells (56%). Most of the units in this class had a powerful inhibitory surround which decreased the activity generated at the field center and in some cases gave rise to firing when stimulated alone. II. On-off center cells (16%). These gave on-off responses to static stimulation. More than half of them had an inhibitory surround which suppressed both on and off discharge, or in other cases either the on or the off burst of the center response. This group of cells also responded strongly to motion independently of direction. III. Cells sensitive only to motion (28%). The discharges to movements of units in this class were not affected by the direction of motion. The visual properties of the thalamic units are discussed in conjunction with previous results in the optic tectum of the pigeon.

Animals↗